The present invention relates generally to a system for sensing the position of an elevator in an elevator shaft in order to allow accurate control of elevator movement and stopping at selected floors. The position information can be used in conjunction with an elevator control system which controls elevator car movement according to input from the sensing system.
Various elevator position sensing systems have been proposed in the past for providing elevator position information to an elevator controller. Some of these systems involve running a coded tape along the length of the elevator shaft and mounting suitable sensors on the elevator car for sensing holes in the tape, for example, and using the sensed hole position to derive elevator position information. Where these systems are reliant on incremental counting from a detected floor position, loss in power to the system results in loss of the collected position data. Additionally, some of the known systems do not provide sufficient accuracy in the detected position information. Some of these problems can be overcome or reduced by a system which determines absolute position of a car in a hoist way or elevator shaft.
One absolute position measurement apparatus is described in U.S. Pat. No. 3,963,098 of Lewis, et al. In this apparatus a tape is provided with two tracks of punched holes arranged to form a digital code in each direction. The code is selected to provide, for any N consecutive bits of data, a bit pattern which is unique and thus which can be used to derive elevator position information. A tape reader on the elevator car reads at least 16 consecutive bits defined by the indicia disposed immediately adjacent the car, and the bit pattern is translated into a car location. The tape reader includes a pair of readers for each track, for reading the information when the car is moving up and when the car is moving down, respectively.
U.S. Pat. No. 4,433,756 of Caputo, et al. describes an elevator system in which a tensioned tape is provided with informational data in two tracks, one of the tracks having a series of uniformly spaced openings and the other track having both uniformly spaced openings and a binary code. The uniformly spaced openings in the second track separate the code into 16-bit increments, and are used to generate a 5 position reading each time 16 consecutive bits of data have been collected. Between these positions, car position is determined by incrementing the car position reader each time an interrupt is provided by the readers directed at the first track. This is susceptible to loss of information in the event of a power failure, and also has an accuracy limited to the spacing between the holes in the first track.